Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.25   11.450%   $275.5601   $275.56   $275.55   $275.60  
  Purchase #2 $71.77   7.541%   $77.1822   $77.18   $77.20   $77.20  
  Purchase #3 $160.54   8.399%   $174.0238   $174.02   $174.00   $174.00  
  Purchase #4 $173.30   12.332%   $194.6714   $194.67   $194.65   $194.70  
  Purchase #5 $228.26   11.725%   $255.0235   $255.02   $255.00   $255.00  
  Purchase #6 $148.33   7.395%   $159.299   $159.30   $159.30   $159.30  
  Purchase #7 $118.80   13.173%   $134.4495   $134.45   $134.45   $134.40  
  7 purchase totals = $1,148.25       $1,270.2095   $1,270.20   $1,270.15   $1,270.20